1. Field of the Invention
The present invention relates to antennas; more particularly, patch antennas.
2. Description of the Prior Art
FIG. 1 illustrates an exploded view of a prior art patch antenna assembly. Front housing 10 and rear housing 12 form the outer surfaces of the antenna assembly. The two sections of the housing enclose multi-layered feedboard 14, resonators 16 and 18 and spacers 20. Spacers 20 are attached to front side 22 of feedboard 14 by screws 24. Screws 24 mate with threads on the inside of spacers 20 by passing through holes 26 in feedboard 14. Resonators 16 and 18 are attached to spacers 20 in a similar fashion. Screws 28 mate with threads on the inside of spacers 20 by passing through holes 30 in resonators 16 and 18. The spacers are chosen so that they provide a space of approximately {fraction (1/10)} of a wavelength between feedboard 14 and resonators 16 and 18. The assembled feedboard, spacers and resonators are mounted inside of the enclosure formed by front housing 10 and rear housing 12. A signal to be transmitted by the antenna assembly is provided to conductor 40 of multi-layered feedboard 14. Conductor 40 is typically positioned on one layer of feedboard 14 such as on top layer 42. An insulating layer is typically provided between conductor 40 and a ground plane layer of feedboard 14. The ground plane layer normally has openings or slots 44 which allow the signal from conductor 40 to couple to resonators 16 and 18 so that the signal can be transmitted through front housing 10.
FIG. 2 provides a more detailed illustration of the assembled feedboard 14, spacers 20 and resonators 16 and 18. Screws 24 pass through holes in feedboard 14 to mate with the threaded inside portion of spacer 20. Similarly, screws 28 pass through holes in resonators 16 and 18 to mate with the threaded inside portion of spacers 20.
This prior art patch antenna assembly suffers from several shortcomings. The assembly is expensive to assemble because of the many individual parts such as eight spacers and 16 screws. The spacers are expensive to mass produce because they include threaded inner portions. Additionally, the holes made through resonators 16 and 18 to allow screws 28 to mate with spacers 20 create unwanted patterns in the radio frequency energy radiated by the antenna assembly. For example, if the antenna is being used for a horizontally polarized transmission, the holes introduce additional non-horizontal polarizations in the transmitted signal.
The present invention provides an inexpensive, easy to assemble patch antenna that does not introduce unwanted polarizations in the transmitted radio-frequency (RF) energy. A feedboard, spacer and resonator are held in a compressed relationship by two halves of the antenna housing. The spacer is a thermo-formed sheet with semi-spherical spacers. The spacers have a height that provides the desired spacing between the feedboard and the resonator.
In one embodiment, spherical spacers are positioned between the feedboard and resonator using an adhesive and then the feedboard, spacers and resonators are held in position by compression provided by the antenna housing assembly.